The main goal of our research during the last 2.5 months has been the production, identification and characterization of hybridoma clone-produced monoclonal antibodies against squamous carcinoma cell lines. Ten million Colo-16 squamous carcinoma cells and a similar number of SH-1 (squamous carcinoma of the upper esophagus) cells were injected intraperitoneally into BALB/c mice. The immunization was repeated 2 weeks later. Five days after the second tumor cell inoculum, the mice were sacrificed and their spleen cells hybridized. Only half of the plated wells had viable hybrids. Of those, 15 were reactive against Colo-16. Six of these 15 were highly reactive and were selected for cloning. We identified 57 reactive supernatants against Colo-16 (out of 576 tested). Thirty-seven of these supernatants (66%) also were reactive against SH-1. Ten of the 37 were highly reactive against both targets. All the reactive supernatants are being tested against a panel of nonsquamous carcinoma and lymphoblastoid cell lines. This approach will help us select the clones with more restricted and promising reactivity. The selected clones will then be grown up for further characterization and analysis by injecting BALB/c mice with viable hybridoma clones. The approach to developing monoclonal antibodies makes use of new developments in molecular biology and is based on the premise that tumor cell DNA can transform mouse fibroblasts and confer to them properties of malignant cells. These cells may express cell surface determinants which are associated with malignant transformation and which may influence the behavior of malignant cells. Preliminary results have suggested the presence of anti-HSV antibodies in the sera of patients with squamous cancer of the oral cavity and oropharynx compared to healthy control. Significant differences in the binding ability of patients and control sera was noted only when sera absorbed with Kaolin was used. Patients with oral cancer do not have an unusually high incidence of herpes virus infections and, therefore, we theorized that the tumor cell may express the viral or highly cross-reactive antigens. These results suggest that the antigenic structure recognized by the monoclonal antibodies recognized antigenic structures which seem to be expressed in a variety of established tumor cell lines. We feel now that testing patients' serum or tumor cells for reactivity against monoclonal antibodies to HSV-1 is less likely to contribute to the diagnosis and/or understanding of the disease.